Position Detector

ABSTRACT

A method for diagnosing a position detector used in determining the position of a control means. The position detector includes a resistance track, and a first terminal in connection with its first end, and a second terminal in connection with second end of the resistance track, and a slide electrically connected to the resistance track. The slide is arranged to move in relation to the control by the effect of a position change. Additionally, the position detector includes a slide terminal in connection with the slide, an electricity supply, a voltage measurer and a signal processing unit for diagnosing measurement data. In the method, a supply voltage is arranged in the slide terminal, the output voltage of the first terminal is measured, the output voltage of the second terminal is measured, and at least a first and a second output voltage are arranged to the signal processing unit.

FIELD OF THE INVENTION

The invention relates to a method for diagnosing a position detectoraccording to the preamble of the appended claim 1. In addition, theinvention relates to a position detector according to the preamble ofthe appended claim 5.

BACKGROUND OF THE INVENTION

Position sensors based on a potentiometer are generally used in formingthe position data of structures and parts of various vehicles andworking machines. Typically, turning the structure of a device turns thepotentiometer, thus creating a change in the resistance of an adjustableresistor. A change in the resistance is interpreted as a change in theposition of the structure, which in some applications leads to a certainfunction. For example, in a vehicle a change in the position of the gaspedal has an effect on the gasoline feed system.

In several uses it is very substantial that no malfunctions occur.Because of this, component securing is used in several applications. Forexample, the movement of a gas pedal can be measured by two or moresensors, in which case the damaging of one sensor does not necessarilylead into a malfunction.

Different solutions have also been developed for condition monitoring ofindividual potentiometers. One such solution is disclosed in patentpublication U.S. Pat. No. 6,184,695, which discloses a diagnosticcircuit for a potentiometric sensor. The main principle of the solutionaccording to the publication is that an alternating voltage is suppliedto the sliding contact of an adjustable resistor, by means of which theresistance of the sliding contact is determined. On the basis of theresistance value it is possible to monitor the condition of theadjustable resistor. The solution in question is, however, relativelycomplex and it only reveals the changes in the resistance of theadjustable resistor.

SUMMARY OF THE INVENTION

Now, a solution has been invented, which enables a versatile conditionmonitoring of a potentiometric sensor in a simple manner.

To attain this purpose, the method for diagnosing a position detectoraccording to the invention is primarily characterized in what will bepresented in the characterizing part of the independent claim 1. Theposition detector according to the invention, in turn, is primarilycharacterized in what will be presented in the characterizing part ofthe independent claim 5. The other, dependent claims will present somepreferred embodiments of the invention.

The basic idea of the invention is that the voltage supply of theadjustable resistor is connected to a slide and voltage is measured fromboth ends of the resistance track. The voltage of the ends changesaccording to the position of the slide, in which case the position datacan be determined on the basis of the voltages of one or both ends.There are advantageously suitable resistances between the ends andground plane (ground reference potential).

The solution according to the invention enables monitoring the cords ofa potentiometer in such a manner that disconnections are detected.

Another embodiment of the invention enables monitoring the cords of apotentiometer in such a manner that short-circuited connections aredetected.

An embodiment of the invention, in turn, enables supplying apotentiometer with an alternating voltage without that substantiallyaffecting the position data.

An embodiment of the invention enables measuring the contact resistanceduring normal operation and provides advance information on the wear ofthe potentiometer. This information can be used, for example, inanticipatory condition monitoring.

By using in some applications the structure according to an embodimentof the invention, the potentiometer does not necessarily have to besecured with several potentiometers, because even a damagedpotentiometer can provide position data that is sufficient for severalapplications.

DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail withreference to the appended principle drawings, in which

FIG. 1 shows a connection according to the invention,

FIG. 2 shows a connection according to FIG. 1 supplemented with thesymbols for voltages and currents,

FIG. 3 shows a connection according to FIG. 1 supplemented with theprinciple structure of the control means, and

FIG. 4 shows some malfunctions that may occur in connecting with apotentiometer 1.

For the sake of clarity, the figures only show the details necessary forunderstanding the invention. The structures and details that are notnecessary for understanding the invention, but are obvious for anyoneskilled in the art, have been omitted from the figures in order toemphasize the characteristics of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a connection according to the basic idea of the invention.In addition, FIG. 2 shows the symbols for currents and voltages, whichare hereinafter used in connection with formulas. FIG. 3, in turn, showsan embodiment, wherein the control means 4 is arranged to control theadjustable resistor 1 and especially its sliding means 11.

The supply voltage V_(S) of the adjustable resistor 1 is brought to theslide terminal T_(S), i.e. the supply terminal, whose contact resistanceis marked with reference R_(S) in the figure. The slide terminal T_(S)is via the sliding means, i.e. the slide 11 connected to a resistancetrack 12, whose resistance is marked with reference R in the figure.From the output terminals at the ends of the resistance track 12, i.e.from the first terminal T₁ and the second terminal T₂, are measured theoutput voltages U₁ and U₂. The voltages U₁, U₂ of the ends changeaccording to the position of the slide 11, in which case the positiondata can be determined on the basis of the output voltages U₁, U₂ of oneor both ends. There are advantageously suitable resistances R_(L)between the ends and ground plane GND. The measurement of the outputvoltages U₁ and U₂ can be implemented in various ways and in the figuresthe measuring means is marked with reference 2. The measurement resultsare forwarded to a signal processing unit 3, which performs thenecessary modifications on the measurement results and processes them inthe desired manner. The signal processing unit 3 may, for example,perform the calculations presented hereinafter. In addition, the signalprocessing unit 3 may application-specifically perform other functionsas well. In the example, only the information of the output voltages U₁,U₂ are shown to be coming to the signal processing unit 3, but naturallythe signal processing unit may be in contact with more means in order toreceived different kinds of information and in order to forward theinformation further.

FIGS. 1, 2 and 3 show the possible series resistance in connection withvoltage supply V_(S) with dashed lines. The series resistance inquestion is not substantial from the point of view of the basic idea ofthe invention, but by using the series resistance it is possible, interalia, to protect the device from malfunctions risks caused by a shortcircuit. Typically, a series resistance is used in variousinstallations.

On the basis of the output voltages U₁, U₂ of the ends of the connectionit is possible to determine direction data α of the slide 11, forexample, in the manner described hereinafter. According to Kirchhoffslaws, the position data of the slide 11 can be determined according tothe following formulas:

$\begin{matrix}{U_{1} = {\frac{R_{L}}{R_{L} + {\alpha \; R}}U_{0}}} & \left. 1 \right) \\{U_{0} = {{{{I_{2}\left( {1 - \alpha} \right)}R} + U_{2}} = {{\frac{U_{2}}{R_{L}}\left( {1 - \alpha} \right)R} + U_{2}}}} & \left. 2 \right)\end{matrix}$

By placing U₀ according to formula 2 into formula 1, the value of theangle is:

$\begin{matrix}{\alpha = \frac{{\frac{R_{L}}{R}\left( {U_{2} - U_{1}} \right)} + U_{2}}{U_{1} + U_{2}}} & \left. 3 \right)\end{matrix}$

In one case the values of the output voltages U₁ and U₂ are ⅔-1×V_(S),when R=5 kΩ and R_(L)=10 kΩ. Thus, approximately only ⅓ of the area ofthe AND converter is in efficient use. It is, however, possible to setthe reference voltage of the converter in such a manner that the area ofthe converter can be utilized better. Also, the magnitudes of R andR_(L) can have an effect on the range of use. For example, when R_(L)=1kΩ, the range of use is 1/7-1×V_(S). Thus, however, the magnitude of thecurrent traveling through the slide 11 increases.

Next, the contact resistance R_(S) is solved. The formula 1 can also bepresented in the form:

$\begin{matrix}{\alpha = \frac{{U_{0}R_{L}} - {U_{1}R_{L}}}{U_{1}R}} & \left. 4 \right)\end{matrix}$

In addition, it is known that:

I ₀ =I ₁ +I ₂  5)

which formula can further be derived to the form:

$\begin{matrix}{U_{0} = {V_{s} - {\frac{R_{s}}{R_{L}}U_{1}} - {\frac{R_{s}}{R_{L}}U_{2}}}} & \left. 6 \right)\end{matrix}$

By placing the U₀ according to formula 6 into formula 4, the followingformula can be formed

$\begin{matrix}{\alpha = \frac{{\left( {V_{S} - U_{1}} \right)R_{L}} - {\left( {U_{1} + U_{2}} \right)R_{s}}}{U_{1}R}} & \left. 7 \right)\end{matrix}$

If both U₁ and U₂ are acceptable, formulas 3 and 7 provide the sameresults. I.e.

$\frac{{\frac{R_{L}}{R}\left( {U_{2} - U_{1}} \right)} + U_{2}}{U_{1} + U_{2}} = \frac{{\left( {V_{S} - U_{1}} \right)R_{L}} - {\left( {U_{1} + U_{2}} \right)R_{s}}}{U_{1}R}$

From which R_(S) can be solved either to the form

$\begin{matrix}{{R_{s} = \frac{{V_{s}{R_{L}\left( {U_{1} + U_{2}} \right)}} - {U_{1}{U_{2}\left( {{2R_{L}} + R} \right)}}}{\left( {U_{1} + U_{2}} \right)^{2}}}{or}} & \left. 8 \right) \\{R_{s} = {{\frac{V_{S}}{U_{1} + U_{2}}R_{L}} - {\frac{U_{1}U_{2}}{\left( {U_{1} + U_{2}} \right)^{2}}\left( {{2\; R_{L}} + R} \right)}}} & \left. 9 \right)\end{matrix}$

depending on which of the previous forms is a better example, forexample, from the point of view of data processing.

The solution according to the invention also enables monitoring theterminals T_(S), T₁, T₂ and the cords of the potentiometer 1 in such amanner that disconnections are detected. By means of the connectionaccording to the invention it is possible to detect such a damageconnected to any connection terminal T_(S), T₁, T₂ of the potentiometer,which would cause the connection terminal not to be able tosubstantially conduct electricity.

FIG. 4 shows some possible malfunction modes C1 to C11 that may occur inconnecting a potentiometer 1. The malfunction modes C1 to C11 include,inter alia, resistance changes, breaks and short circuits, which mayoccurs, for example, in the connecting points of the potentiometer 1and/or other connection connected to it and in cable portions. Table 1shows a summary of short descriptions of the described malfunctions, thepossibility of detecting malfunctions and the possibility of identifyingmalfunctions, as well as the status of the measuring accuracy of thepotentiometer 1 during the malfunctions in question.

TABLE 1 Detecting and identifying some malfunction modes and the effectof malfunctions on the function Measuring Case Description ofmalfunction Detected Identified accuracy C1 Change in contact Yes Yesnormal resistance C2 Break in terminal T₁ Yes Yes reduced C3 Break interminal T_(S) Yes No not functioning C4 Break in terminal T₂ Yes Yesreduced C5 Mutual short circuit of Yes Yes not terminals functioning C6Short circuit of terminals Yes Yes not T₁ and T₂ functioning C7 Shortcircuit of terminals Yes Yes reduced T₁ and T_(S) C8 Short circuit ofterminals Yes Yes reduced T₂ and T_(S) C9 Short circuit of terminal YesYes reduced T₂ to ground C10 Short circuit of terminal Yes No not T_(S)to ground functioning C11 Short circuit of terminal Yes Yes reduced T₁to ground

In malfunction mode C1 the contact resistance R_(S) has changed. Thus,ranges of magnitudes of both the first output voltage U₁ and the secondoutput voltage U₂ have changed. Since the changes in the voltage areasare similar, i.e. the area has either lowered or risen, the malfunctioncan be detected and identified. Since the direction data α is determinedon the basis of the output voltages U₁ and U₂, the potentiometer 1functions normally for the part of the direction data. The detectiondata of malfunction can be utilized in anticipatory conditionmonitoring, in which case the malfunction is repaired at a suitablemoment. Typically when the slide 11 of the potentiometer 1 and/or theresistance track 12 wears, the value of the contact resistance R_(S)rises and at the same time, there is notable variance in its value, onthe basis of which a malfunction of the potentiometer 1 can beanticipated.

In malfunction mode C2, in turn, the first terminal T₁ is damaged, inwhich case the first output voltage U₁ goes substantially near the 0volt of the ground plane (or near some other basic value of ground planeGND in use). Direction data α can thus, if necessary, be determined bymeans of only one output voltage U₂.

In malfunction mode C3 the connection terminal T_(S) of the slide isdamaged, in which case both U₁ and U₂ go substantially near the 0 volt(or near some other basic value in use). Thus, only the malfunction canbe detected, but in malfunction mode C3 it is not possible to determinethe type of the malfunction more specifically, nor the direction data α.

In malfunction mode C4, when the second terminal T₂ is damaged, thesecond output voltage U₂, in turn, goes substantially near the 0 volt(or near some other basic value of ground plane GND in use). Directiondata α can thus, if necessary, be determined by means of only the firstoutput voltage U₁.

An embodiment of the invention also enables monitoring the cords andconnection terminals T_(S), T₁, T₂ of the potentiometer 1 in such amanner that short circuited connections are detected. By means of theconnection according to the invention it is possible to detect anyshort-circuit-type of damage C5 to C11 of a connection point T_(S), T₁,T₂ of the potentiometer 1. For example, if all three connectionterminals T_(S), T₁, T₂ are in short circuited with the supply voltageV_(S), i.e. malfunction mode C5, the output voltages U₁ and U₂ gosubstantially close to the supply voltage V_(S). Thus, when changing theposition of the slide 11, the values of the output voltages U₁ and U₂ donot change, and direction data α cannot be formed. Malfunction mode C5can be detected and identified, but the formation of the direction dataα is not successful.

Correspondingly, in malfunction mode C6 the terminals T₁ and T₂ are inshort circuited, in which case when changing the position of the slide11, the values of the output voltages U₁ and U₂ do not change, anddirection data α cannot be formed. Also, malfunction mode C6 can bedetected and identified, but the formation of the direction data α isnot successful.

In malfunction mode C7, the first terminal T₁ is short circuited withthe supply voltage V_(S), in which case the first output voltage U₁ goessubstantially close to the supply voltage V_(S). Thus, when the positionof the slide 11 is changed, the value of the first output voltage U₁does not change, but the value of the second output voltage U₂ changes.Direction data α can thus, if necessary, be determined by means of onlyone output voltage U₂. I.e. malfunction mode C7 can be both detected andidentified and the direction data α can be formed.

Correspondingly, when the second terminal T₂ is short circuited with thesupply voltage V_(S), i.e. malfunction mode C8, the value of the secondoutput voltage U₂ goes substantially close to the supply voltage V_(S).Thus, when the position of the slide 11 is changed, the value of thefirst output voltage U₁ changes, but the value of the second outputvoltage U₂ does not change. Direction data α can thus, if necessary, bedetermined by means of only the first output voltage U₁.

In malfunction mode C9, the terminal T₂ is short circuited with groundplane, in which case the second output voltage U₂ goes substantiallynear the 0 volt (or near some other basic value of ground plane GND inuse). Thus, when the position of the slide 11 is changed, the value ofthe second output voltage U₂ does not change, but the value of the firstoutput voltage U₁ changes. Direction data α can thus, if necessary, bedetermined by means of only the first output voltage U₁. I.e.malfunction mode C9 can be detected and identified, and thepotentiometer 1 functions with a reduced resolution.

Correspondingly, in malfunction mode C11, the first terminal T₁ is, inturn, short circuited with ground plane, the first output voltage U₁goes substantially near the 0 volt (or hear some other basic value ofground plane GND in use). Thus, when the position of the slide 11 ischanged, the value of the first output voltage U₁ does not change, butthe value of the second output voltage U₂ changes. Direction data α canthus, if necessary, be determined by means of only one output voltageU₂.

When the terminal T_(S) of the slide 11 is short circuited with groundplane, i.e. malfunction mode C10, both the first output voltage U₁ andthe second output voltage U₂ go substantially near the 0 volt (or nearsome other basic value of ground plane GND in use). Thus, the directiondata α cannot be determined. Only the malfunction can be detected inmalfunction mode C10, but not the more specific type of the malfunction.

As can be detected from the above-described examples, by means of thestructure according to the invention, it is possible to detect shortcircuits and supply breaks. In, malfunction modes of the first or secondterminal T₁, T₂, it is still possible to form direction data α, if it isnecessary.

Detection data and identification data of malfunctions can be utilizedin anticipatory condition monitoring. Thus, such malfunctions and wearthat is likely to lead to malfunctions, which do not have an effect onthe operation of the potentiometer, can be fixed at a suitable moment.For example, a potentiometer 1, whose wear is detected from changes inthe contact resistance R_(S) (malfunction mode C1) can be changed at asuitable time before it actually malfunctions. On the other hand, someof the malfunctions have an effect on the normal operation of thepotentiometer 1, but enable the controlled finishing of the functions.These malfunction modes include, for example, C2, C4, C7, C8, C9 andC11.

By combining, in various ways, the modes and structures disclosed inconnection with the different embodiments of the invention presentedabove, it is possible to produce various embodiments of the invention inaccordance with the spirit of the invention. Therefore, theabove-presented examples must not be interpreted as restrictive to theinvention, but the embodiments of the invention may be freely variedwithin the scope of the inventive features presented in the claimshereinbelow.

1-9. (canceled)
 10. A method for diagnosing a position detector, whichposition detector is used in determining the position of a controlmeans, which position detector comprises a resistance track, a firstterminal in connection with the first end of the resistance track, asecond terminal in connection with the second end of the resistancetrack, a slide means electrically connected to the resistance track,which means is arranged to move in relation to the resistance track bythe effect of a change in the position of the control means, a slideterminal in connection with the slide means, electricity supply, avoltage measuring means, and a signal processing unit for diagnosing themeasurement data, the method comprising: arranging a supply voltage inthe slide terminal; measuring an output voltage of the first terminal;measuring an output voltage of the second terminal; and arranging atleast a first and a second output voltage for the signal processingunit.
 11. The method according to claim 10, wherein the position of thecontrol means is determined on the basis of the first output voltage andthe second output voltage.
 12. The method according to claim 10, whereinat least a part of the malfunctions of the position detector areidentified on the basis of the first output voltage and the secondoutput voltage.
 13. The method according to claim 10, wherein themagnitude of the range of the first output voltage and the second outputvoltage is affected by resistances, which are placed between the firstterminal and ground plane and between the second terminal and groundplane.
 14. A position detector for determining a position of a controlmeans, the position detector comprising: a resistance track; a firstterminal in connection with the first end of the resistance track; asecond terminal in connection with the second end of the resistancetrack; a slide means electrically connected to the resistance track,which means is arranged to move in relation to the resistance track bythe effect of a change in the position of the control means; a slideterminal in connection with the slide means; electricity supply; avoltage measuring means; and a signal processing unit for diagnosing themeasurement data, wherein the supply of a supply voltage is arranged inthe slide terminal, the first terminal is connected to the voltagemeasuring means to measure the first output voltage, the second terminalis connected to the voltage measuring means to measure the second outputvoltage, and at least a first and a second output voltage are arrangedfor the signal processing unit.
 15. The position detector according toclaim 14, wherein the signal processing unit is arranged to determinethe position of the control means on the basis of the first outputvoltage and the second output voltage.
 16. The position detectoraccording to claim 14, wherein the signal processing unit is arranged toidentify at least a part of the malfunctions of the position detector onthe basis of the first output voltage and the second output voltage. 17.The position detector according to claim 14, wherein detector inaddition comprises a potentiometer, which comprises at least aresistance track and a slide means.
 18. The method according to claim14, wherein the position detector in addition comprises ground plane andat least two resistances, which are placed between the first terminaland ground plane and between the second terminal and ground plane, inorder to affect the range of the first output voltage and the secondoutput voltage.